Method to reduce sensitivity of a magnetic read-write head to external magnetic fields

ABSTRACT

In a read-write head, the shields can serve as magnetic flux conductors for external fields, so that they direct a certain amount of flux into the recording medium. This problem has been overcome by the addition to the shields of a pair of tabs located at the edges closest to the ABS. These tabs serve to prevent flux concentrating at the edges so that horizontal fields at these edges are significantly reduced. Said tabs need to have aspect ratios of at least 2 and may be either triangular or rectangular in shape. Alternatively, the tabs may be omitted and, instead, outer portions of the shield&#39;s lower edge may be shaped so as to slope upwards away from the ABS.

This is a divisional application of U.S. patent application Ser. No.11/117,672, filed on Apr. 28, 2005, which is herein incorporated byreference in its entirety, and assigned to a common assignee.

FIELD OF THE INVENTION

The invention relates to the general field of magnetic disk systems withparticular reference to magnetic write heads for perpendicular designsand their sensitivity to external magnetic fields.

BACKGROUND OF THE INVENTION

As magnetic recording is pushed to higher areal densities, perpendicularrecording may offer advantages in thermal stability over longitudinalrecording, thus delaying arrival at the super-paramagnetic limit.Another advantage of perpendicular recording with single pole (SP) headand perpendicular media, with a soft underlayer (SUL), is the ability toproduce a larger write field than that of a ring head to record onrelatively thick media with high anisotropy constant.

A typical read-write unit is illustrated in FIG. 1. Seen there are yoke11, write coil 12, return shield 14, and lower write shield 15. Writingis performed in the vertical direction by write pole 13 into softunderlayer and recording medium 16 (shown as a single layer) for the PMR(perpendicular magnetic recording) configuration shown here. Reading isperformed by unit 19 which is typically a giant magneto-resistance (GMR)or a tunneling magnetic junction (TMJ) device.

The magnetic components of writer shield 14 as well as reader shields 17and 18 can serve as magnetic flux conductors for external fields, sothat they direct a certain amount of flux into soft underlayer andrecording medium 16. When the flux density is large enough, unwantedwriting or erasing can occur. Because of the magnetic softness of theshield materials, a small amount of external field can induce relativelylarge fields in the media and cause erasure of information on the media.

In most current PMR designs, shields 14, 17 and 18 have a strictlyrectangular shape as seen in FIG. 2 which is a view of FIG. 1 along thedirection of arrow 20. Due to the finite thickness and moment of thesoft magnetic underlayer, flux distribution is not uniform over thesurfaces of the shields. At the sharp corners and edges, the fluxdensity can be much higher than that at the shield center. In general,data under a shield corner is usually erased first.

A routine search of the prior art was performed with the followingreferences of interest being found:

In U.S. Pat. No. 6,757,141, Santini et al. disclose a flare on thebottom FM shaping layer and the top FM probe layer of the second polepiece where the flare point widens after the ABS. In U.S. Pat. No.5,075,280, Pisharody et al. show surfaces of the pole portions chamferedto slope away from the plane of the recording medium. Pole shields areformed on the chamfered surfaces of the pole portion of the core.

Parker et al. teach a shield having an edge adjacent to the ABS in U.S.Patent Publication 2003/0227714 while Okada et al. describe a recessedshield to prevent leaking of the magnetic field in US Patent Publication2003/0026039. Kuroda et al. show a shield formed to a required shape inUS Patent Publication 2003/0021063 and Mori et al. teach patterning ashield layer to an appropriate size in US Patent Publication2001/0017753.

SUMMARY OF THE INVENTION

It has been an object of at least one embodiment of the presentinvention to provide a magnetic read-write head.

Another object of at least one embodiment of the present invention hasbeen that said read-write head be insensitive to the presence ofexternal magnetic fields.

A further object of at least one embodiment of the present invention hasbeen to provide a method for forming said read-write head.

These objects have been achieved by:

1) The addition of a pair of tabs located at the edges closest to theABS. Said tabs need to have an aspect ratio of at least 2 and may beeither triangular, rectangular, other polygon in shape.2) Removal of sharp edges so as to create a shallow recess angle, saidremoved region needs to have an aspect ratio of at least 2.3) Any combination of (1) and (2)

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a magnetic read-write head of the prior art.

FIG. 2 shows a read element shield of the prior art.

FIG. 3 shows a pair of triangular tabs appended to a shield.

FIG. 4 shows a pair of rectangular tabs appended to a shield.

FIG. 5 illustrates a recessed edge.

FIG. 6 illustrates a shield having both a tab and a recessed edge.

FIG. 7 shows plots for the structures seen in FIGS. 3 and 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention solves the problem of excessive fields at shieldedges by modifying their shape to include extra tabs or to createrecessed edges at their lower (ABS) edges. In the case of extra tabs,the shape of these tabs may be either triangular (as in tabs 31 in FIG.3) or rectangular (as in tabs 41 in FIG. 4). In the case of recessededges, the angle of recessed edges is a constant, with respect to theABS line (as shown in FIG. 5. Typically, the angle of the slope would bebetween about 8 to 20 degrees and outer portion 63 should constituteless than 30% of shield width. FIG. 6 shows yet another embodiment whichis a combination of tabs (71) and recessed edge (73).

In FIG. 7, the magnetic field in the media under a constant externalfield of 200 Oe is plotted as a function of position along the shieldfor a conventional rectangular shield (curve 81), a shield withtriangular tab (curve 82), and a shield with a recessed edge (curve 83).It is clear that the peak of the magnetic field occurs at the edge ofthe shield.

By introducing the tab, or a recessed edge, the concentration of flux atthe edge is avoided and fields at the edges can be significantlyreduced. In the calculation shown in FIG. 7, a length of L of 3 micronsand a height H of 1 micron were used for the triangular tab (curve 82)and for the recessed edge (curve 83). In both cases, the erasing fieldat the outer edge of the tab or recessed edge is smaller than the fieldat the shield center. As already noted, for the tab or recessed edge tobe effective, a larger valued of L/H is preferred.

To enable full reproduction of the invention, the following additionalinformation is provided:

-   -   Each tab has a length that is at least 2 times its height    -   The height of each tab is between about 0.1 and 10 microns    -   The length of each tab is between about 0.2 and 20 microns    -   Each tab is made of the same material and thickness as its        associated shield    -   Each recessed edge has a slope angle between 5 and 20 degrees    -   Each recessed edge has a recessed length of between about 0.2        and 20 microns.    -   Suitable materials for the shield include Ni, Fe, Co alloys,        such as NiFe, CoFeNi.    -   Each shield has a height that is between about 10 and 50 microns    -   Each shield has a thickness that is between about 0.5 and 5        microns

What is claimed is:
 1. A method to reduce sensitivity to externalmagnetic fields of a magnetic read-write head, comprising: providing aperpendicular magnetic writer having an ABS, a magnetic read head havingan ABS that is coplanar with said writer ABS, magnetic reader and writershields on opposing sides of said read head, one of said second magneticshields being located between said perpendicular magnetic writer andsaid magnetic read head, all shields having lower horizontal edges thatare parallel to said ABS, and opposing vertical edges that are normal tosaid ABS; attaching to each shield a magnetically soft tab having a topedge that extends away from said vertical edge and, at said verticaledge, giving said tab a height that is less than that of its associatedshield and a lower edge that is an extension of said lower horizontaledge; and giving each tab a triangular shape by sloping each tab's topedge towards its lower edge so as to meet said lower edge at its pointof termination, whereby flux concentration and horizontal magneticfields are reduced at said shield's edges.
 2. The method of claim 1wherein each tab has a length that is at least 2 times its height atsaid vertical edge.
 3. The method of claim 1 wherein erasing fields atsaid shield's edges are reduced in magnitude by about 30% relative toerasing fields present in the absence of said tabs.
 4. The method ofclaim 1 wherein each tab has a length that is between about 0.2 and 20microns.
 5. The method of claim 1 wherein each tab has a height at saidvertical edge that is between about 0.1 and 10 microns.
 6. The method ofclaim 1 wherein each shield has a height that is between about 10 and 50microns.
 7. The method of claim 1 wherein each tab is of the samematerial and thickness as its associated shield.
 8. The method of claim1 wherein each shield has a thickness that is between about 0.5 and 5microns.
 9. A method to reduce sensitivity to external magnetic fieldsof a magnetic read-write head, comprising: providing a perpendicularmagnetic writer having an ABS, a magnetic read head having an ABS thatis coplanar with said writer ABS, magnetic reader and writer shields onopposing sides of said read head, one of said second magnetic shieldsbeing located between said perpendicular magnetic writer and saidmagnetic read head, all shields having lower horizontal edges that areparallel to said ABS, and opposing vertical edges that are normal tosaid ABS; and attaching to each shield a magnetically soft rectangulartab having a top edge that extends away from said vertical edge andgiving said tab a height that is less than that of its associated shieldand a lower edge that is an extension of said lower horizontal edge,whereby flux concentration and horizontal magnetic fields are reduced atsaid shield's edges.
 10. The method of claim 9 wherein each tab has alength that is at least 2 times its height at said vertical edge. 11.The method of claim 9 wherein erasing fields at said shield's edges arereduced in magnitude by at least 30% relative to erasing fields presentin the absence of said tabs.
 12. The method of claim 9 wherein each tabhas a length that is between about 0.2 and 20 microns.
 13. The method ofclaim 9 wherein each tab has a height that is between about 0.1 and 10microns.
 14. The method of claim 9 wherein each shield has a height thatis between about 10 and 50 microns.
 15. The method of claim 9 whereineach tab is of the same material and thickness as its associated shield.16. The method of claim 9 wherein each shield has a thickness that isbetween about 0.5 and 5 microns.